The building of the Lower Thames Crossing has been thrown into doubt following the Prime Minister’s failure to commit to part of the HS2 project.

Rishi Sunak faced backlash this week after suggestions he was looking to scrap the northern section of the high-speed rail line that would link London to Manchester.

The news has raised questions over other big infrastructure projects including the Lower Thames Crossing.

The controversial project aims to reduce congestion at the Dartford Crossing by building a 2.6 mile tunnel connecting Kent and Essex. It is currently being considered for a development consent order by the planning inspectorate.

In March the Department for Transport delayed the project by two years and when asked this week by KentOnline if there were any plans to scale back or cancel the plans a spokesman reiterated its statement from then.

They said: “As one of the largest planning applications ever, the Lower Thames Crossing, backed by £800 million to date, will also be slowed down by 2 years. This will allow more time to take into account stakeholder views and prepare an effective and deliverable plan, while helping to meet inflationary pressures and deliver the planning processes properly.”

In July, the government was told by the all-party House of Commons select committee on transport to think carefully about hugely expensive projects.

The committee said: “In the face of increasing costs, looming net zero commitments and an ageing network in need of maintenance, the department needs to ensure that future road investment strategy portfolios are deliverable. It is time for the government to reconsider its portfolio of expensive, complex SRN [strategic road network] enhancement projects.”

Transport analyst Stephen Joseph, a visiting professor on transport solutions at Hertfordshire University, told the Guardian: “Much of the focus has been on HS2 but there are other projects that must now be in doubt, particularly the Lower Thames Crossing, which is very expensive and which has not seen any spades sunk in the ground yet.”

Laura Blake, chair of Thames Crossing Action Group, which opposes the project, said: “We believe there is plenty of evidence to show that the crossing should not go ahead. It fails to meet its objectives, and would not solve the problems at the Dartford Crossing, which would still remain overcapacity.

“It would be hugely destructive and harmful, including a whopping 6.6m tonnes of carbon emissions. The cost has risen from £4.1bn up to £9bn as of August 2020, and we believe it will now be in excess of £10bn and a complete waste of taxpayers’ money.”

As the party conference begins today in Manchester, Rishi Sunak is expected to focus on other measures to help motorists including filling potholes, rather than commenting on the future of any big new schemes.